As copying and scanning of color hard-copy documents becomes more prevalent in the business world, there has arisen a need for full-color solid-state photosensitive devices, such as a silicon chip having an array of photosensors thereon. One prior-art for causing the photosensors on the silicon chip to be sensitive to a specific primary color is to provide, on the main surface of the silicon chip, a layer of spectrally transparent filter material, such as polyimide or acrylic, which has been dyed or pigmented to a specific primary color. If a single photosensitive chip is intended to have multiple linear arrays of photosensors, each linear array being sensitive to one particular primary color, particular polyimide layers are applied to specific linear arrays, thereby creating a full-color photosensitive chip.
One typical method of construction of full-color photosensitive chip is to first create a wafer having a relatively large number, such as one hundred or more, of semiconductor structures, each structure corresponding to one chip. Filters are applied to the structures on the wafer so that filter areas will be applied to the desired linear arrays of photosensors on each chip structure. Typically this application of filter material is carried out by applying an even layer of translucent liquid to the entire wafer, developing the desired areas of the filter material with a photo mask, and then etching away the translucent material in all other areas. For full-color chips, multiple layers of translucent filter material are applied to the wafer, and then etched away as needed, to yield the three primary-color-filtered linear arrays of photosensors. Only after the filter layers are applied as desired is the wafer “diced,” or sawed into individual chips. According to one technique, the chip termination is a combination of chemically-etched v-groove and a mechanically sawed portion. The diced chips are first tested and screened for defective chips, and the usable chips are then abutted into a longer linear array.
In the construction of full-color photosensitive chips having translucent filter layers attached thereto, certain practical problems are evident. One problem concerns the inadvertent ripping or other damage to the cured filter layers when the wafer is diced into individual chips: the relatively thin translucent filter layer, particularly at the photosensors toward either end of the chip, can be torn by the action of a saw blade. If the translucent color filter is torn in a manner that even a very small portion (as little as 1%) of the area of one photosite is exposed to unfiltered white light, this extra light thus introduced to the photosite will have an appreciable effect on resulting image quality. It is therefore crucial that the translucent filters be placed on a wafer from which chips are created such that the integrity of the filters is maintained throughout the manufacturing process.